The farmer whose workers discovered the body, after an employee drove over it in a combine harvester, said he initially thought it was a rolled-up mattress.

Colin Rayner, deputy mayor of Windsor and Maidenhead, who runs the farm, said the body was discovered when workers were reaping a field of oil seed rape.

He told The Chronicle: "The chap who was carting the oil seed rape noticed something left behind, I saw the body myself at about 5pm but I thought it was a rolled-up mattress and didn't give it a second thought.

"It was only when one of the workers went back for a closer look that he realised what it was. My chaps were so upset they asked me to phone the police for them."

Mr Rayner said the fast-growing crop was planted last September and would have been about two feet tall by March this year, meaning workers would not have seen a body despite regularly spraying the field.

Anyone with information is asked to call the new non-emergency police number 101 or Crimestoppers, free and anonymously, on 0800 555 111.